1. Field of the Invention
This invention relates to a method for characterizing a surface utilizing electrochemically generated current flows through an ultra microelectrode type tip near a surface of a substrate immersed in a solution. In particular, the invention relates to scanning the tip relative to the surface to characterize contour and composition features of the surface.
2. Description of Related Art
The scanning electrochemical microscope marginally resembles the scanning tunneling microscope in its use of a tip to scan a surface of a substrate material. A scanning tunneling microscope depends upon the flow of a tunneling current between the tip and the substrate. The distance between the tip and substrate is typically of the order of one nanometer (nm) or less. Topographic resolution is typically of this size scale, i.e. of the order of nanometers. In scanning tunneling microscope applications where the substrate is in solution, the tunneling current is a nonfaradaic one; that is, no chemical changes in solution components or substrate surface species occur due to the current flow. Because the current is nonfaradaic, the current through the tip cannot be related directly to the substrate potential by consideration of the redox potentials of appropriate half reactions.
As used throughout this document, the term substrate refers to a material, and particularly a surface of a material, preferably being scanned utilizing the present invention. Further, as used throughout this document, the positioning of a tip substantially perpendicular to a surface refers to positioning the tip in a manner that a line may be drawn substantially perpendicular to the surface that will substantially perpendicularly intersect a small cross-sectional area of the tip at which electrochemical reactions preferably occur. Also as used throughout this document, connecting an electric potential between a tip and a substrate may include connecting an electric potential between a tip and an auxiliary electrode and connecting an additional potential between the auxiliary electrode and the substrate producing a potential between the tip and the substrate. A reference electrode is preferably used to measure the potential of the tip and the substrate. As used throughout this document, the positioning of a tip proximate to a surface refers to positioning the tip in the range of approximately less than one tip diameter from the surface to approximately eight tip diameters from the surface.